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Cooling mods for 1998 Prado Turbo Diesel 3.0 1KZ-TE


New Member
Jul 23, 2023
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I made a post in a thread about this subject that has had no replies for 3 years. As I expected, I did not get anything for replies. So I have created a new post in the hopes I get a response.

I have had a 98 Prado intercooled auto turbo diesel for a few months now, and I am intending to get it prepared for some towing and 4x4ing.
As far as I can see, it is pretty stock. I am going to give it a full tune up, and make some changes to the cooling system.
I live in Canada, where summer can reach 35 degrees and winter can reach -35 degrees.

Before I get into that something else I have noticed so far:
I go through nearly liter of oil over about 1200-1500km, no leaks on the driveway where I park, but there is some visible slight leakage from the top of the hose where it clamps around the connecting pipe of the intercooler on the turbo side. Seems as though it only does this while highway driving. Would replacing the hose, and getting better (non-spring) retaining clips sort this? Or am I looking at some other issue?

Onto cooling/monitoring:

I intend to add some gauges, what is the best recommendation between EGT, Oil pressure, coolant temp, and transmission temp? is an 'all-in-one' gauge reasonable?

I will replace the thermostat with a 76 degree one.

I will replace my 7-fin fan with a 10-fin fan.

Viscous hub seems like it is functioning properly, but I will likely buy some oil and make sure it is 100%.

A new radiator is likely in my future if I can find one at a decent price (seems hard in North American, suggestions are welcome!). It has been recently flushed. A new rad cap is probably a good idea, as well as new rad hoses.

Changing to a 3" dump seems to be a good idea, but I question whether the whole exhaust should be 3" considering the lack of back pressure that would create. Is there anywhere that offers a 3" dump that would connect directly to the existing exhaust? Or is a 3" dump rather easily adapted to the stock exhaust?

Am I missing anything?

I am also intending to delete the EGR and give the manifold and throttle-body a good cleanse.

Thanks to all who have some insight!
For some reason or another engines burn oil from day one and engines like what could be described as a comfort zone where you top your oil up to spot on the full mark go for a thousand miles drive and its used a litre of oil so you top it up and do the same thing again and again and again and keep using oil now leave the oil level where it is and do your daily routine check of fluids after a while you should see the oil level will stay steady in its comfort zone if the level drops drastically then you know you have a problem found this out when I was a truck driver doing two thousand km a week the mechanic just told me leave it see what happens and keep some oil with you
When I got my automatic 97 Colorado the first thing I did was replace the radiator, thermostat, water pump, viscous hub and hoses with new genuine Toyota parts as preventative maintenance. I’ve also replaced the top and bottom ball joints with genuine Toyota parts.
A few years ago, while on a trip in the Pyrenees mountains, we almost cracked the head due to overheating (the ambient temperatures at the time were 42°C/107°F). Fortunately, I managed to get home to the UK intact. After poking around in the engine bay a bit, I removed the original viscous fan and opened it up to find that it was almost bone dry. I replaced the fan with a new one and replaced the 82° thermostat with the 76° one. That was about 2 years or so back. Anyway, we are off to the Italian Alps in a few days, and I couldn’t help but become a little paranoid over the new fan, so at the weekend I removed it and opened it up as I had read that many people have said that even when new, the fans were underfilled. While it did have some oil in it, I decided just to add some more and put another bottle’s worth in, though I kind of wish I had two bottles because it could definitely use more. At the same time as I had the radiator cowl off, I decided to back spray the radiator out to ensure the vents were as clear as possible. If we make it there and back without overheating again, I will call it a success and will be greatly relieved. For me, this will be a ‘getting back on the horse’ kind of moment and hopefully restore my confidence!
It's not supposed to be 'full' by design, it is a measured (cc) amount of correct weight/viscosity oil - oil of the correct type is used in r/c models which is often easier and cheaper to source.
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It's not supposed to be 'full' by design, it is a measured (cc) amount of correct weight/viscosity oil - oil of the correct type is used in r/c models which is often easier and cheaper to source.
There was no fear of it being anywhere near full Tractionman, there wasn't much to start with. At least it now has one bottles worth of the correct fluid in there. Hopefully, it will help.
I have a 3.4 petrol so different engine but one of the first additions I did when I base-lined the truck was adding a coolant temp gauge on the top rad tube, really quick to install and you have constant real undampened reading of your coolant temp. it also gives me the peace of mind of knowing the thermostat is working well. the 5vzfe seems to run a top temp of 91C, highest I've seen is 92C when worked hard.
tangentially as my transmission has failed and it's in for a rebuild (going in later this week) I am adding an ATF temp gauge too and an external atf cooler too...
I have a 2002 1kz-te prado manual i am located in Australia gets very hot here as well
Our old girl has never used oil in 380,000 klm so if it has ever gotten hot from say a blown head like ours it may have cracked a piston
Our first head replacement was at 148500 klm and was not under warranty and at that time we were flat broke
So i was servicing the car every 5000 klm
So new head
2 nd cracked head 300,000 & had head off for a week whilst sourcing and working between jobs
And found a crack in the top ring area of no 2 piston was noticeable from top of piston
So poss could be something like this
Or change oil to valvoline and see if it improves
I also did pistons and rings with a hone at same time what a head £ucx the pistons are numbered on the yop and you have to order them from toyota or the top to head clearance will be incorrect as i found out the hard way 1 set of aftermarket pistons an 1 new head latter bang ,bang rattle rattle rattle top of pistons collide with head and stuffed that idea
Ordered a new set from toyota and put in
An d new head no2 as with the impact it most deffinatley would have cracked
Success stage 2 turbo & 3 bar maf sensor
Water to air intercooler & most important thing 10 blade fan and new ebay spec alloy 3 core radiator spaced towards engine with some 12 mm spacers
I used 12 mm nuts
To allow air between ac condensor and radiator cooling fins wow what a difference work carried out over a year it also has a 3” exhaust & dump pipe and Dp chip it is do far the best 1kz-te i have driven not yet dynoed but feels luke it has about 105 kwand drives so well i never want to part with it
16 psi boost 40degree days int cairns “ Top end of australia “heaps of humidity and can sit on 120 klmh and also tow a 2.3 tonne van at speed limits and ip hills and it has never gotten hot again
The 3 core Radiator and new fan made a huge difference but also replace the fan clutch if it has done over 150,000 klm just to be sure
I also replaced the thermostat with a 73deg instead of the 86 degree that was origionally in it
Any how enough from me i hope you find something of worth in my rambles
I haven't read through all the previous posts but my personal theory is that back pressure from an inadequate down pipe causes overheating .

all turbo's run incredibly hot and the 1kz-te turbo is water , oil and air cooled and so everything is good so long as your cooling system , turbo and downpipe are in pristine condition .

Mileage and years are no indicator of when or why it might become a problem because of the incalculable variable of driving style . In my own mind a taxi driver or driving instructor is more likely to suffer the dreaded cracked head than a boy racer or getaway driver .

Not sure why anyone would go to the trouble of replacing the down pipe with 3" and then reducing back to the factory exhaust because the downpipe is the difficult bit . But i suppose it would help to move the bottleneck away from the turbo allowing for some general cooling by passing airflow .

My 3" exhausts include a muffler and produce a sound that turns heads with a smile of appreciation rather than a frown of consternation .

After 3" exhaust was fitted a new radiator a 73 degree thermostat and a k&n air filter I towed a heavy trailer through Germany all day at 70 to 100 mph up some very steep hills and as a result never got around to fitting the EGT gauge i'd bought , just don't feel i need it any more .